So, let's get this straight . Black hole evaporation is, by the layman's version, supposedly due to a negative mass particle entering the black hole, while it's counterpart leaves, as radiation. These particles are formed near the black hole by vacuum fluctuations (i.e. pair production). I'm not entirely certain, but when a pair is formed in vacuum fluctuations, I've always assumed they both had positive mass (since antimatter and matter both have positive mass when real). So I have a contradiction here. Is it something to do with the fact that they are virtual particles? But even so, what allows a virtual particle to have negative mass? What's going on here?